As for existing electrical outlets, the jacks are generally exposed. If metal objects or other conductive bodies are brought accidentally into contact the metal sheet in the jack, serious safety hazards exist due to possible electric shock and leakage.
To resolve this problem, the electrical outlets have been modified in the design work, such as a flapper is arranged in front of the jack; when connected with the plug, the pin of the plug can be inserted into the jack by pushing off the flapper; when the pin is removed, the flapper can be reset automatically to seal the jack. Such design could improve the safety of electrical outlet to some extent. However, in case where the flapper isn't fully reset during frequent operation, some metal objects are possibly inserted into the jack, leading to safety hazards arising from electric shock and leakage.